1. Field of the Invention
The present invention relates generally to the conditioning of semiconductor surfaces and, more particularly, to the passivation of such semiconductor surfaces, that is, the elimination of minority carrier recombination via surface states. Specifically, the present invention relates to the passivation of Group III-V or II-VI semiconductor surfaces utilizing a passivating material which is specifically lattice mismatched to the principal semiconductor material.
2. Description of the Prior Art
It has become a relatively standard procedure to form heterostructures of Group III-V and Group II-VI semiconductor materials by utilizing well-known epitaxial growth techniques such as molecular beam epitaxy or metalorganic chemical vapor deposition. Considerable effort has been committed to the characterization of structural properties of these heterostructures in terms of dislocations, defects, and crystal strain as well as of transport and electro-optical properties of the grown layers.
A particular application of such heterostructures involves the surface passivation of Group III-IV semiconductors. The passivation of Group III-V semiconductor surfaces, that is, the elimination of minority carrier recombination via surface states using high-bandgap window layers, has traditionally been limited to materials systems that are nearly perfectly lattice matched. Lattice matching has been found to be necessary in the past in order to eliminate interface states and thus provide effective passivation of the principal semiconductor material. The necessity for such lattice matching has severely limited the number of materials systems which can benefit from window layer passivation.
One example of epitaxial growth of a window material on the surface of a semiconductor substrate is illustrated in an article entitled "Effects of ZnSe Epitaxial Growth on the Surface Properties of GaAs", Applied Physics Letters 51(18), 2 Nov. 1987, pgs. 1422-1424. In this particular disclosure, it is shown that the formation of ZnSe/GaAs heterostructures results in effective passivation of the GaAs surface due to the extremely close lattice matching between the passivating material (ZnSe) and the principal semiconductor material (GaAs).
The successful use of significantly lattice-mismatched materials for passivation would substantially increase the number of materials systems which can benefit from window layer passivation, as well as possibly reduce the cost thereof due to the use of readily available materials. Although efforts in their vein have been attempted in the past, the resultant semiconductor devices have not been particularly effective due to the deleterious effects of lattice mismatch. Heteroepitaxy of lattice-mismatched materials is generally deemed to be undesirable due to the high density of dislocations created in the grown layers. Dislocations form in order to reduce the interfacial strain between the lattice mismatched layers and significantly reduce the performance of semiconductor devices formed therein. Consequently, while the use of closely lattice-matched materials for passivation provides highly efficient semiconductor devices, the effective use of significantly less closely lattice-matched materials would have several advantages, including a wider selection of materials combinations and, in some cases, reduced cost. Thus, there still remains a need to provide a system or method for passivating semiconductor surfaces which is low in cost, readily achievable, and applicable to a wide spectrum of semiconductors.